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CDPHE Graywater Characteristics

The Colorado Department of Public Health and Environment, or CDPHE, defines graywater as water that is drained from baths, showers, washing machines and kitchen sinks and reused for irrigation or landscapes. The reuse of graywater in Colorado is controlled by county Individual Sewage Disposal System regulations and is not always legal in Colorado because of potential public health issues.

  1. Graywater and Blackwater

    • CDPHE regulations apply to both graywater and blackwater or toilet wastes as the same; graywater is usually of higher quality than blackwater, regulations do not separate the two. In some states, kitchen sink, garbage disposal and dishwasher water is considered blackwater because of the high concentrations of organic waste. Neither graywater nor blackwater is considered safe to reuse in Colorado. When water is reused in surface or subsurface applications, the person reusing it must be permitted. Once a permit is issued, monitoring by county or state agencies is usually required.

    Nutrients

    • Graywater is desirable to many people for use to irrigate landscapes because it often contains nitrogen or phosphorous, which are important nutrients for plants. People who use graywater for landscape plants (not edible plants) filter the water before using it whether it is applied to the surface or the subsurface. Filtering and reusing graywater is also desirable because it conserves treated tap water, which often does not have the same nutrients as filtered graywater.

    Pathogens

    • Graywater, especially that which is used in baths and for washing dishes, usually contains bacteria and other pathogens that are dangerous to the environment, people and animals. Warm up water -- water that has left the water heater and is run down the drain without being used for bathing or washing dishes -- is generally free of harmful pathogens. CDPHE recommends catching this water in a bucket for use in landscapes to conserve water. In some homes, where no recirculation system is connected to the water heater, this is a good source of uncontaminated water.

    Sodium and Chloride

    • Graywater applied to surface landscapes can be dangerous to sensitive plant species because it can contain high amounts of sodium and chloride. CDPHE admits that research on the public health issues related to reuse of graywater is limited and data available does not indicate problems or non-problems. Sometimes the use of graywater requires the installation of advanced treatment systems.

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